Certain passengers must breathe additional oxygen at any time or at all times during a flight independently of the current operational status of the emergency oxygen supply system. This requirement for additional oxygen occurs particularly when the cabin pressure is lower than the normal atmospheric pressure at sea level, but not low enough to trigger the operation of the emergency oxygen supply. Such persons may require additional oxygen during the entire flight time and during times while sitting in the aircraft on the ground. For this purpose it is customary to use chemical oxygen generators, portable oxygen bottles or tanks, or portable oxygen generators known as OBOGS (on board oxygen generator system). These additional oxygen sources and their respective distribution systems are not permanently installed in an aircraft and require installation and maintenance when an aircraft is prepared for its next flight.
This disclosure distinguishes between an emergency oxygen supply and a therapeutic oxygen supply made available for passengers who require extra oxygen.
Certain types of aircraft have a permanently installed therapeutic oxygen supply system including a therapeutic oxygen source installed at a certain location within the aircraft. The distribution of therapeutic oxygen is performed through a separate conduit system connected to oxygen taps in the aircraft cabin. These oxygen taps are constructed for connecting therapeutic oxygen breathing masks to the taps for passengers who require such a therapeutic oxygen supply service.
It is also conventional to have small portable oxygen supply bottles on board for those passengers that only have a temporary breathing problem for which they require additional oxygen.
There are basically four conventional approaches for the supply of therapeutic oxygen to aircraft passengers. Chemical oxygen generators for supplying therapeutic oxygen to passengers require repeated installation, removal, and maintenance work including safety checks. Such chemical oxygen generators must be triggered either manually or automatically. Further, systems with chemical oxygen generators require the installation of more or fewer generators, depending on the flight duration and on the estimated number of passengers that may want to use therapeutic oxygen. Once chemical oxygen generators have been activated it is not possible to deactivate such generators, whereby the produced oxygen that is not used for the therapeutic services, is wasted. If a decompression of the cabin pressure occurs, in response to which the emergency oxygen system is activated, the user of the therapeutic oxygen supply system must exchange the therapeutic oxygen breathing mask against an emergency oxygen breathing mask. The passengers need to be instructed accordingly and in an emergency, confusion may result as to which mask is which.
Similar considerations apply to the use of portable oxygen bottles for the supply of therapeutic oxygen. Such bottles have their own masks which must be exchanged against the emergency oxygen breathing mask when the cabin pressure drops below the predetermined level. Additionally, portable oxygen supply bottles need a control that is responsive to the current cabin pressure. Such control must be explained to the user which also may result in confusion. The foregoing considerations also apply to portable oxygen generators (OBOGS). Here again a switch between different oxygen breathing masks is required when the emergency oxygen system becomes effective.
Similar considerations apply to a permanently installed therapeutic oxygen supply system which also has its own separate oxygen masks that must be exchanged for emergency oxygen masks when the emergency oxygen supply system becomes effective in response to a failed cabin pressure.